Environmental cues and dietary antioxidants affect breeding behavior and testosterone of male European starlings (Sturnus vulgaris)

Environmental cues, such as photoperiod, regulate the timing of major life-history events like breeding through direct neuroendocrine control. Less known is how supplementary environmental cues (e.g., nest sites, food availability) interact to influence key hormones and behaviors involved in reproduction, specifically in mi- gratory species with gonadal recrudescence largely occurring at breeding sites. We investigated the behavioral and physiological responses of male European starlings to the sequential addition of nest boxes and nesting material, green herbs, and female conspecifics and how these responses depend on the availability of certain antioxidants (anthocyanins) in the diet. As expected, cloacal protuberance volume and plasma testosterone of males generally increased with photoperiod. More notably, testosterone levels peaked in males fed the high antioxidant diet when both nest box and herbal cues were present, while males fed the low antioxidant diet showed no or only a muted testosterone response to the sequential addition of these environmental cues; thus our results are in agreement with the oxidation handicap hypothesis. Males fed the high antioxidant diet maintained a constant frequency of breeding behaviors over time, whereas those fed the low antioxidant diet decreased breeding behaviors as environmental cues were sequentially added. Overall, sequential addition of the environmental cues modulated physiological and behavioral measures of reproductive condition, and dietary antioxidants were shown to be a key factor in affecting the degree of response to each of these cues. Our results highlight the importance of supplementary environmental cues and key resources such as dietary antioxidants in enhancing breeding condition of males, which conceivably aid in attraction of high quality females and reproductive success

Schematic representation of the design of Assay I.

<p>Schematic representation of the design of Assay I and the way of calculating pre-zygotic isolation mechanisms under male competition index on the example of a female’s line 1. Procedures are described in the text.</p

Mate choice and post-zygotic isolation indexes for monogamous and promiscuous mating system.

<p>Mean mate choice and post-zygotic isolation indices for monogamous and promiscuous mating system calculated from the mean indices for male lines. Indices values lower than 0.5 indicate that a female from the same line as a male produces on average more offspring than a female from a different line. Bars indicate 95% confidence intervals.</p

Schematic representation of the design of Assay II.

<p>Schematic representation of the design of Assay II and the way of calculating mate choice and post-zygotic reproductive isolation on the example of a male’s line 1. Procedures are described in the text.</p